The Saints beat Neil Lennon's men 2-1 at McDiarmid Park in September and while they lost 5-0 when the two sides met in the Scottish Communities League Cup quarter-final at Parkhead the following month, Lomas men grabbed a 1-1 draw in the SPL when they returned to the east end of Glasgow in November.
St Johnstone's efforts have barely dented Celtic in their title quest - the champions are 18 points clear of Motherwell at the top of the table - but they have shown the way to the rest of the SPL.
However, the Northern Irishman will not reflect too long on the four points won against the Hoops, who are fresh from a 6-2 hammering of Dundee United at the weekend.
Lomas said: "We are not looking at it like that, we are looking at playing a very good Celtic team.
"They have players like Gary Hooper, Kris Commons, Joe Ledley, Victor Wanyama, Anthony Stokes - the list is endless.
"We will go into the game massive underdogs and it will take another mammoth effort from everyone if we are to get anything.
"When you play the Old Firm you have got to be at your maximum.
"You have to be disciplined, be brave in and out of possession, have a little bit of luck and take your chances when they come along.
"If Celtic get their noses in front then it is very difficult. They bounced back from the Juventus defeat to thrash Dundee United and they can do that against anybody on their day.
"But we are one of eight or nine teams who want to be up there behind them and we are looking forward to the game."
Lomas, though, admits he is still puzzled by Ross County manager Derek Adams' analysis of the Staggies' 1-0 win over Saints in Dingwall on Saturday, which left the Perth side in sixth place.
The former West Ham and Manchester City midfielder said: "I read some of Derek's quotes and he said his side dominated. I'm not sure where he got that from.
"I suppose football is all about opinions but their keeper was man of the match.
"On any other day we could have got three points and it just goes to show you that stats can lie.
"On every stat we were ahead but in the one stat that mattered, they got the goal.
"Their keeper made a few good saves, they had defenders getting blocks in and so all credit to them but I thought we were the better team."